Since inflatable occupant restraint systems have come into widespread use in the automotive industry, it has been observed that there are certain instances in which it may be desirable to deactivate the airbag system, or a portion thereof. Exemplary of such an instance is that present when a rear-facing infant seat is placed in the front passenger position and is not properly positioned for use with the airbag. Another example is that of a driver who is small in stature and must operate a vehicle from a seating position that is very close to the steering wheel of the vehicle.
Airbag systems have been developed which include a manually actuated switch for deactivating the airbag for the passenger seat and/or driver seat positions. It is known to provide a visual indicator such as a lamp to indicate to occupants of the vehicle when one or both of the airbags are deactivated. See, for example, U.S. Pat. No. 5,992,880, the disclosure of which is incorporated herein by reference.
It is also known to provide an airbag system in which either airbag may be disabled automatically depending upon one or more inputs from sensors in the vehicle passenger compartment. For example, it is known to provide a weight sensor in the passenger seat and institute control logic which turns OFF or disables the passenger side airbag automatically when a weight below a certain threshold level is present in the passenger seat. The threshold weight level may be selected to constitute a cut-off line between a large-statured person, for whom normal airbag operation is considered appropriate, and a small statured person, for whom the airbag should be disabled. An indicator lamp is illuminated when the airbag is OFF to provide confirmation to the driver and the passenger of the fact that the airbag is disabled.
The above-described control logic may be further configured so that when the passenger seat weight sensor detects a weight below a second, lower threshold value (for example, 15 lbs.), the seat is considered to be completely unoccupied, as opposed to occupied by a small-statured person. In this case, the airbag is disabled because it is not needed, but the lamp is not illuminated because the driver does not require positive confirmation of the airbag being disabled. The lower threshold value is preferably not zero so that relatively light objects such as grocery bags, packages, purses, or the like may be set on the passenger seat without unnecessarily illuminating the "airbag off" lamp.
One possible shortcoming inherent in the above-described system may become apparent if a light-weight infant carrier seat containing a small infant is placed in the passenger seat and secured in place for travel. The total weight of the seat and infant will be less than the upper threshold, so that the airbag is disabled, as is appropriate. However the weight may also be below the lower threshold value so that the "airbag off" lamp is not illuminated, and hence the driver is not provided with any positive confirmation that the airbag is disabled.
It is also known to provide an airbag circuit which includes a sensor for determining the status of the seat belt buckle so that the operation of the airbag system may be adjusted depending on whether the occupant is belted or unbelted. See for example U.S. Pat. No. 5,982,048.